Grinding Concrete High Spots Before Flooring

Grinding can be one method of reducing localized concrete high spots, but the appropriate method depends on the slab, how much correction is involved, the flooring system's requirements, the equipment available and the conditions on site.

The work is a series of small removals with a check after each one — not a single pass aimed at making the slab look perfect.

1. Identify the high area on the exposed, clean slab.
2. Mark it, including where it actually stops rather than where it looks worst.
3. Compare it with the surrounding floor, so you know what plane you are working toward.
4. Decide whether grinding is an appropriate correction for this slab, this material and this amount of correction.
5. Prepare the work area and protect adjacent finishes and rooms.
6. Control dust appropriately for the equipment and the space.
7. Remove material gradually rather than in one aggressive pass.
8. Vacuum and clean so you can see and measure the surface.
9. Recheck flatness with a straightedge in more than one direction.
10. Repeat cautiously only if the recheck says more is needed.

Do not grind simply because one location looks high. A spot can read high because the floor around it dips, because a straightedge is bridging two other points, or because the check was made in only one direction. Establish the surrounding plane before removing anything.

Marking and measuring technique is covered in flatness vs. level, and the filling side in floor patch and low spots.

Grinding is subtractive and one-directional. Take too much off and the hump becomes a depression that now has to be filled — usually with more material, more time and more added height than the original correction would have taken.

• Work toward the surrounding plane, not toward a visually perfect slab.
• Stop and check often rather than checking once at the end.
• Treat the marked area as the target, and keep the edges blended into what is around them.
• Reassess the whole floor after a significant removal, because the reference has moved.
• Accept that some correction may be better handled with fill than with more grinding.

There is no universal amount of concrete that can be safely removed from a slab. Reinforcement depth, slab thickness, construction and the condition of the concrete all vary, and a significant removal is a question for someone who can evaluate the slab on site.

Concrete grinding generates a large amount of fine dust and involves powered equipment with real hazards. Plan for both before the machine is switched on.

FloorGauge does not specify a respirator rating or state exposure figures. Those are set by the applicable safety requirements for the work and the equipment being used.